Settable, form-filling loss circulation control compositions comprising in situ foamed calcium aluminate cement systems and methods of using them

ABSTRACT

This document relates to settable, hydraulic, non-Portland foamed cement compositions comprising nitrogen gas-generating compositions used for loss circulation control.

TECHNICAL FIELD

This document relates to settable, foamed hydraulic non-Portland cementcompositions comprising a nitrogen gas-generating compound used for losscirculation control.

BACKGROUND

Natural resources such as gas, oil, and water in a subterraneanformation are usually produced by drilling a well bore down to asubterranean formation while circulating a drilling fluid in thewellbore. Fluids used in drilling, completion, or servicing of awellbore can be lost to the subterranean formation while circulating thefluids in the wellbore. In particular, the fluids may enter thesubterranean formation via depleted zones, zones of relatively lowpressure, lost circulation zones having naturally occurring fractures,weak zones having fracture gradients exceeded by the hydrostaticpressure of the drilling fluid, and so forth.

One of the contributing factors may be lack of precise information onthe dimensions of loss circulation areas, which can range frommicrofractures to vugular zones. Depending on the extent of fluid volumelosses, loss circulation is classified as seepage loss, moderate loss,or severe loss. For oil-based fluids, losses of 10-30 barrels per hourare considered moderate, and losses greater than 30 barrels per hour areconsidered severe. For water-based fluids, losses between 25 and 100barrels are considered moderate, and losses greater than 100 barrels areconsidered severe. For severe losses, the dimensions of the losscirculation zones cannot be estimated which makes it difficult to designloss circulation treatment pills based on the sized particles. Therevenue loss due to loss circulation materials (LCM) problems extendsinto tens of millions of dollars.

Loss circulation treatments involving various plugging materials havebeen used to prevent or lessen the loss of fluids from wellbores. Theideal loss circulation treatment solution will have to be adaptable toany dimension or shape of the loss circulation zone. Thus, there is aneed for a composition that can form-fill upon placement, irrespectiveof the shape and size of the thief zone.

SUMMARY

Provided herein are foamed cementitious compositions. The compositionsare hydraulic non-Portland cementitious compositions that includecalcium aluminate; a nitrogen gas-generating compound; an amineactivator; and a foam surfactant. In some embodiments, the calciumaluminate comprises greater than or about 68.5% alumina and less than orabout 31% calcium oxide.

In some embodiments of the cementitious compositions, the foamsurfactant is selected from the group consisting of an alkyl sulfatesalt with a C₁₂-C₁₄ carbon chain, a betaine, a hydroxysultaine, andcombinations thereof. In some embodiments, the foam surfactant iscocoamidopropyl hydroxysultaine.

In some embodiments of the cementitious compositions, the nitrogengas-generating compound is an azo compound. In some embodiments, the azocompound is azodicarbonamide. In some embodiments, the azo compound isabout 1% to about 10% by weight of the calcium aluminate.

In some embodiments, the amine activator is selected from the groupconsisting of carbohydrazide (CHZ) and tetraethylenepentamine (TEPA). Insome embodiments, the weight ratio of the azo compound to the amineactivator is about 5:1 to about 1:5. In some embodiments, the amineactivator is CHZ.

In some embodiments, the cementitious composition further includes a setretarder selected from the group consisting of hexametaphosphate, sodiumborate, sodium citrate, citric acid, and an aminophosphonate.

In some embodiments, the cementitious composition further includes aviscosifier.

In some embodiments, the cementitious composition further includes afiller.

In some embodiments, the composition does not include an oxidizer.

In some embodiments, the composition does not include calcium silicates.In some embodiments, the composition is not Portland cement.

Also provided herein is a foamed cementitious composition that includescalcium aluminate comprising greater than or about 68.5% alumina andless than or about 31% calcium oxide; azodicarbonamide in an amount ofabout 1% to about 10% by weight of the calcium aluminate; an amineactivator, wherein the weight ratio of the azo compound to the amineactivator is about 5:1 to about 1:5; and a foam surfactant.

In some embodiments, the amine activator is selected from amongcarbohydrazide and TEPA.

In some embodiments, the cementitious composition further includes aviscosifier.

Also provided herein is a method of treating a loss circulation zone ina subterranean formation. In some embodiments, the method includes: a)forming a foamed cementitious composition that contains calciumaluminate; a nitrogen gas-generating compound; an amine activator; and afoam surfactant; and b) introducing the foamed cementitious compositioninto the loss circulation zone.

In some embodiments of the method, the nitrogen gas-generating compoundis an azo compound. In some embodiments, the azo compound is about 1% toabout 10% by weight of the calcium aluminate.

In some embodiments of the method, the amine activator is selected fromthe group consisting of carbohydrazide (CHZ) and tetraethylenepentamine(TEPA). In some embodiments, the weight ratio of the azo compound to theamine activator is about 5:1 to about 1:5.

DESCRIPTION OF DRAWINGS

The FIGURE shows gas generation in a series of cement compositionscontaining various viscosifiers.

DETAILED DESCRIPTION

Reference will now be made in detail to certain embodiments of thedisclosed subject matter. While the disclosed subject matter will bedescribed in conjunction with the enumerated claims, it will beunderstood that the exemplified subject matter is not intended to limitthe claims to the disclosed subject matter.

Values expressed in a range format should be interpreted in a flexiblemanner to include not only the numerical values explicitly recited asthe limits of the range, but also to include all the individualnumerical values or sub-ranges encompassed within that range as if eachnumerical value and sub-range is explicitly recited. For example, arange of “about 0.1% to about 5%” or “about 0.1% to 5%” should beinterpreted to include not just about 0.1% to about 5%, but also theindividual values (for example, 1%, 2%, 3%, and 4%) and the sub-ranges(for example, 0.1% to 0.5%, 1.1% to 2.2%, and 3.3% to 4.4%) within theindicated range. The statement “about X to Y” has the same meaning as“about X to about Y,” unless indicated otherwise. Likewise, thestatement “about X, Y, or about Z” has the same meaning as “about X,about Y, or about Z,” unless indicated otherwise.

As used herein, the terms “a,” “an,” or “the” are used to include one ormore than one unless the context clearly dictates otherwise. The term“or” is used to refer to a nonexclusive “or” unless otherwise indicated.The statement “at least one of A and B” has the same meaning as “A, B,or A and B.” In addition, it is to be understood that the phraseology orterminology employed in this disclosure, and not otherwise defined, isfor the purpose of description only and not of limitation. Any use ofsection headings is intended to aid reading of the document and is notto be interpreted as limiting; information that is relevant to a sectionheading may occur within or outside of that particular section.

In the methods described herein, the acts can be carried out in anyorder, except when a temporal or operational sequence is explicitlyrecited. Furthermore, specified acts can be carried out concurrentlyunless explicit claim language recites that they be carried outseparately. For example, a claimed act of doing X and a claimed act ofdoing Y can be conducted simultaneously within a single operation, andthe resulting process will fall within the literal scope of the claimedprocess.

The term “about” as used herein can allow for a degree of variability ina value or range, for example, within 10%, within 5%, or within 1% of astated value or of a stated limit of a range.

As used herein, a “cement” can be a binder, for example, a substancethat sets and can bind other materials together. Hydraulic cements(e.g., Portland cement, calcium aluminate cements) harden because ofhydration, chemical reactions that occur independently of the mixture'swater content; they can harden even underwater or when constantlyexposed to wet weather. The chemical reaction that results when the drycement powder is mixed with water produces hydrates that have extremelylow solubility in water.

As used herein, a “cementitious composition” can refer to a hydraulicnon-Portland cement composition. The non-Portland cementitiouscompositions provided herein are calcium aluminate based cements. Thecementitious compositions provided herein exclude Portland cements. A“Portland cement” is a calcium silicate based hydraulic cement. Calciumaluminate cements and Portland cements are made in different manners.For example, a calcium aluminate cement contains calcium and aluminumand oxygen, while Portland cements contain calcium, silicon, aluminumand sulfur. A cementitious composition can also include additives. Thecementitious compositions described herein can include water or be mixedwith water. Depending on the type of cement, the chemical proportions,and when a cement composition is mixed with water, it can hydrate andset to form a single phase hard solid material.

As used herein, the term “set” can mean the process of becoming hard orsolid by curing. Depending on the composition and the conditions, it cantake just a few minutes up to 72 hours or longer for some cementcompositions to initially set.

As used herein, a “retarder” can be a chemical agent used to increasethe thickening time of a cement composition. The need for retarding thesetting of a cement composition by extending the duration during whichthe cement composition remains as a pumpable fluid tends to increasewith the depth of the zone to be cemented due to the greater timerequired to place the slurry in the zone of interest and complete thecementing operation, and to compensate the set acceleration effect ofincreased temperature on the setting of the cement. A longer thickeningtime at the design temperature allows for the longer pumping time thatmay be required.

The term “alkyl” as used herein can refer to straight chain and branchedalkyl groups and cycloalkyl groups having from 1 to about 40 carbonatoms, 1 to about 20 carbon atoms, 1 to about 12 carbons or, in someembodiments, from 1 to about 8 carbon atoms. Examples of straight chainalkyl groups include those with from 1 to about 8 carbon atoms such asmethyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, andn-octyl groups. Examples of branched alkyl groups include, but are notlimited to, isopropyl, iso-butyl, sec-butyl, t-butyl, neopentyl,isopentyl, and 2,2-dimethylpropyl groups. As used herein, the term“alkyl” encompasses n-alkyl, isoalkyl, and anteisoalkyl groups as wellas other branched chain forms of alkyl. Representative substituted alkylgroups can be substituted one or more times with any of the groupslisted herein, for example, amino, hydroxy, cyano, carboxy, nitro, thio,alkoxy, and halogen groups.

The term “amine” as used herein can refer to primary, secondary, andtertiary amines having, e.g., the formula N(group)₃ wherein each groupcan independently be H or non-H, such as alkyl, aryl, and the like.Amines include, but are not limited to, RNH₂, for example, alkylamines,arylamines, alkylarylamines; R₂NH wherein each R is independentlyselected from, for example, dialkylamines, diarylamines, aralkylamines,heterocyclylamines and the like; and R₃N wherein each R is independentlyselected from, for example, trialkylamines, dialkylarylamines,alkyldiarylamines, triarylamines, and the like. The term “amine” alsoincludes polyamines in which the amine contains more than aminofunctional group.

The term “amino group” as used herein can refer to a substituent of theform —NH₂, —NHR, and —NR₂, wherein each R is independently selected, andprotonated forms of each. Accordingly, any compound substituted with anamino group can be viewed as an amine. An “amino group” within themeaning herein can be a primary, secondary, or tertiary amino group. An“alkylamino” group includes a monoalkylamino, dialkylamino, andtrialkylamino group.

The term “room temperature” as used herein can refer to a temperature ofabout 15° C. to about 28° C.

As used herein, the term “polymer” can refer to a molecule having atleast one repeating unit and can include copolymers.

The term “downhole” as used herein can refer to under the surface of theearth, such as a location within or fluidly connected to a wellbore.

As used herein, the term “fluid” can refer to liquids and gels, unlessotherwise indicated.

As used herein, the term “drilling fluid” can refer to fluids, slurries,or muds used in drilling operations downhole, such as during theformation of the wellbore.

As used herein, the term “cementing fluid” can refer to fluids orslurries used during cementing operations of a well. For example, acementing fluid can include an aqueous mixture including at least one ofcement and cement kiln dust. In another example, a cementing fluid caninclude a curable resinous material such as a polymer that is in an atleast partially uncured state.

As used herein, the term “subterranean material” or “subterraneanformation” can refer to any material under the surface of the earth,including under the surface of the bottom of the ocean. For example, asubterranean formation or material can be any section of a wellbore andany section of a subterranean petroleum- or water-producing formation orregion in fluid contact with the wellbore. Placing a material in asubterranean formation can include contacting the material with anysection of a wellbore or with any subterranean region in fluid contacttherewith. Subterranean materials can include any materials placed intothe wellbore such as cement, drill shafts, liners, tubing, casing, orscreens; placing a material in a subterranean formation can includecontacting with such subterranean materials. In some examples, asubterranean formation or material can be any below-ground region thatcan produce liquid or gaseous petroleum materials, water, or any sectionbelow-ground in fluid contact therewith. For example, a subterraneanformation or material can be at least one of an area desired to befractured, a fracture or an area surrounding a fracture, and a flowpathway or an area surrounding a flow pathway, wherein a fracture or aflow pathway can be optionally fluidly connected to a subterraneanpetroleum- or water-producing region, directly or through one or morefractures or flow pathways.

As used herein, “treatment of a subterranean formation” can include anyactivity directed to extraction of water or petroleum materials from asubterranean petroleum- or water-producing formation or region, forexample, including drilling, stimulation, hydraulic fracturing,clean-up, acidizing, completion, cementing, remedial treatment,abandonment, and the like.

As used herein, a “flow pathway” downhole can include any suitablesubterranean flow pathway through which two subterranean locations arein fluid connection. The flow pathway can be sufficient for petroleum orwater to flow from one subterranean location to the wellbore orvice-versa. A flow pathway can include at least one of a hydraulicfracture, and a fluid connection across a screen, across gravel pack,across proppant, including across resin-bonded proppant or proppantdeposited in a fracture, and across sand. A flow pathway can include anatural subterranean passageway through which fluids can flow. In someembodiments, a flow pathway can be a water source and can include water.In some embodiments, a flow pathway can be a petroleum source and caninclude petroleum. In some embodiments, a flow pathway can be sufficientto divert from a wellbore, fracture, or flow pathway connected theretoat least one of water, a downhole fluid, or a produced hydrocarbon.

Compositions and Reaction Products Thereof

Provided in this disclosure are settable, hydraulic, non-Portland cementcompositions, e.g., calcium aluminate based cement compositions,comprising nitrogen-gas generating compounds. The compositions describedherein are in situ foaming compositions that include fast-settingcalcium aluminate cement compositions. Calcium aluminate cementcompositions typically contain variable calcium oxide and alumina molarratios and hydrate rapidly in water to form high strength materials. Theamount of alumina typically ranges from about 40% to about 80%, with theremaining content being calcium oxide. The hydrates formed, depending onthe initial composition of anhydrous calcium aluminate, can includemixtures of 3CaO.Al₂O₃.6H₂O and Al₂O₃.3H₂O, which forms a cohesive massof high strengths. The foamed cementitious compositions can form-fillupon placement, irrespective of the shape and size of the losscirculation zone, to cure loss circulation problems. The foamedcompositions can set up to hard masses to withstand hydrostaticpressures from wellbore fluids without requiring extensive foamequipment that can involve cryogenic nitrogen and the associatedmachinery. Provided herein are calcium aluminate cement-based slurriesthat are foamed with in situ generated nitrogen gas. The gas isgenerated by a nitrogen gas-generating compound. In some embodiments,the compositions comprise an activator or accelerator compound that canaccelerate generation of gas from the gas-generating compound. Thecementitious compositions can also contain other components. Forexample, fillers such as flyashes can be used to reduce the content ofcalcium aluminate.

Provided in this disclosure is a foamed cementitious compositionincluding calcium aluminate, a nitrogen gas-generating compound, and afoam surfactant. Also provided in this disclosure is a foamedcementitious composition that includes calcium aluminate, a nitrogengas-generating compound, an amine activator, and a foam surfactant.

The foamed cementitious compositions provided herein are calciumaluminate based non-Portland cements. In some embodiments, the hydraulicfoamed non-Portland cement compositions described herein include calciumaluminate cements which are a combination of calcium oxide, and alumina.Calcium aluminate cements are hydraulic cements that when mixed withwater harden and set. Any calcium aluminate cement suitable for use insubterranean applications can be used in the compositions describedherein. In some embodiments, the calcium aluminate cement can include acement having an alumina concentration within the range of about 40% toabout 80% of the weight of the calcium aluminate cement. For example,the cement can have an alumina concentration of about 40% to about 75%,about 40% to about 70%, about 40% to about 65%, about 40% to about 60%,about 40% to about 55%, about 40% to about 50%, about 40% to about 45%,about 45% to about 80%, about 45% to about 75%, about 45% to about 70%,about 45% to about 65%, about 45% to about 60%, about 45% to about 55%,about 45% to about 50%, about 50% to about 80%, about 50% to about 75%,about 50% to about 70%, about 50% to about 65%, about 50% to about 60%,about 50% to about 55%, about 55% to about 80%, about 55% to about 75%,about 55% to about 70%, about 55% to about 65%, about 55% to about 60%,about 60% to about 80%, about 60% to about 75%, about 60% to about 70%,about 60% to about 65%, about 65% to about 80%, about 65% to about 75%,about 65% to about 70%, about 70% to about 80%, or about 75% to about80% of the calcium aluminate cement. Examples of suitable calciumaluminate cements include, but are not limited to, commerciallyavailable cements such as those available under the trade names SECAR®51, SECAR® 60, SECAR® 71, SECAR® 712, SECAR® 80, and CIMENT FONDU®,cements commercially available from KERNEOS™ Aluminate Technologies,CA-14 and CA-270, commercially available from ALMATIS™ Premium Alumina.In some embodiments, the calcium aluminate cement is SECAR® 71.

In some embodiments, the calcium aluminate cement can contain one ormore fillers. Suitable examples of fillers include, but are not limitedto, fly ash, sand, clays, and vitrified shale.

In some embodiments, the nitrogen gas-generating compound included inthe cementitious compositions described herein is an azo compound. Insome embodiments the azo compound is a derivative of azodicarboxylicacid with the formula:

where X is independently selected from among NH₂, a monoalkylaminogroup, a dialkylamino group, OH, O⁻M^(n+) (where M^(n+) is an alkali oralkaline earth metal), alkyl, aryl, or an alkoxy group. In someembodiments, the azodicarboxylic acid derivative is selected from anamide derivative, an ester derivative, and an alkali salt of thecarboxylic derivative. In some embodiments, the nitrogen gas-generatingazodicarboxylic acid derivative is azodicarbonamide (AZDC) with thestructure:

In some embodiments, the nitrogen gas-generating azodicarboxylic acidderivative is an ester represented selected from among diisopropylazodicarboxylate (DIAD) and diethyl azodicarboxylate (DEAD) representedby the structures:

In some embodiments, the foamed cementitious composition includes anitrogen gas-generating compound in an amount of about 0.1% to about 20%by weight of the calcium aluminate. For example, the nitrogengas-generating compound can be about 1% to about 10% by weight of thecalcium aluminate or about 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%,5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 11%, 12%, 13%,14%, 15%, 16%, 17%, 18%, 19%, or about 20% by weight of the calciumaluminate.

In some embodiments, the amount of gas generated in the foamed solidcementitious composition is about 65% to about 90% of the foamedcomposition. For example, the amount of gas generated can be about 69%to about 85% of the foamed composition or about 69%, 70%, 71%, 72%, 73%,74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%,88%, 89%, or about 90% of the foamed solid composition.

In some embodiments, the foam surfactant is selected from among an alkylsulfate salt, an alpha-olefin sulfonate, a betaine, a hydroxysultaine,an amine oxide, and combinations thereof. In some embodiments, the alkylsulfate salt has an alkyl chain that is a C₁₂-C₁₄ carbon chain, such assodium dodecyl sulfate. In some embodiments, the foam surfactant iscocoamidopropyl hydroxysultaine. In some embodiments, the foamsurfactant is a combination of an alkyl sulfate salt and cocoamidopropylhydroxysultaine.

In some embodiments, the foam surfactant is present in an amount ofabout 30 wt % to about 50 wt % in an aqueous solution. In someembodiments, the foam surfactant is in an aqueous solution containing awater soluble alcohol, for example isopropyl alcohol. In someembodiments, the foam surfactant is about 30% to about 50% by weight inthe aqueous solution. For example, the foam surfactant can be about 30%,35%, 40%, 45%, or about 50% by weight in the aqueous solution. In someembodiments, the foam surfactant is a 48 wt % solution ofcocoamidopropyl hydroxysultaine in water.

In some embodiments, the surfactant or combination of surfactants isadded in about 1% to about 10% by volume of the mix water used to makethe cement composition. In some embodiments, the surfactant solution isadded in about 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or about 10% by volume ofthe mix water used to make the cement composition.

In some embodiments, the foamed cementitious composition includes anamine activator or accelerator compound. The amine activator/acceleratorcompound can be used to accelerate the generation of gas from thenitrogen gas-generating compound. In some embodiments, the amineactivator is selected from among a hydrazide, a hydrazine, asemi-carbazide, and an ethyleneamine. Examples of suitableethyleneamines include ethylenediamine (EDA), diethylenetriamine (DETA),triethylenetetramine (TETA), and tetraethylenepentamine (TEPA). In someembodiments, the amine activator is TEPA. In some embodiments, the amineactivator is a hydrazine salt. In some embodiments, the amine activatoris hydrazine sulfate. In some embodiments, the amine acceleratorcompound is a hydrazide with the structure:

In some embodiments, the hydrazide is carbohydrazide (CHZ) and R isNHNH₂. In some embodiments, the amine activator is a semi-carbazide withthe structure:

In some embodiments, the semi-carbazide is an unsubstitutedsemi-carbazide and R is H (i.e., hydrazinecarboxamide). In someembodiments, the hydrazide is p-toluenesulfonyl hydrazide.

In some embodiments, the composition comprises a nitrogen gas-generatingcompound that is an azo compound and an amine activator. In someembodiments, the compositions described herein include an azo compoundand a hydrazide. In some embodiments, the composition comprises AZDC andCHZ. In some embodiments, the composition comprises AZDC and TEPA. Insome embodiments, the composition comprises AZDC and hydrazine sulfate.

In some embodiments, the weight ratio of the nitrogen gas-generatingcompound to the amine activator is about 20:1 to about 1:20, such asabout 10:1 to about 1:10, or about 5:1 to about 1:5. For example, theweight ratio of the nitrogen gas-generating compound to the amineactivator can be about 5:1 to about 1:5, about 5:1 to about 1:4, about5:1 to about 1:3, about 5:1 to about 1:2, about 5:1 to about 1:1, orabout 5:1, 4:1, 3:1, 2:1, 1:1, 1:2, 1:3, 1:4, or about 1:5. In someembodiments, the nitrogen gas-generating compound is an azo compound. Insome embodiments, the azo compound is AZDC.

In some embodiments, the foamed cementitious composition includes a setretarder. In some embodiments, set times of calcium aluminate cement ata given temperature can be controlled by set retarders. In someembodiments, the set retarder is selected from among a citrate salt,citric acid, sodium hexametaphosphate, aminomethyleneorganophosphonates, and sodium borate salts. In some embodiments, theset retarder is selected from among sodium hexametaphosphate (SHMP),sodium borate, sodium citrate, citric acid, sodium tetraborate and thepentasodium salt of amino tri(methylene phosphonic acid) (Na₅ATMP). Anexemplary Na₅ATMP salt includes Dequest 2006®, available as a 40%solution from Italmatch Chemicals (Red Bank, N.J.). In some embodiments,the set retarder is SHMP.

In some embodiments, the set retarder is present in an amount of 0.5 wt% to about 10 wt % of the calcium aluminate, or about 1 wt %, 2 wt %, 3wt %, 4 wt %, 5 wt %, 6 wt %, 7 wt %, 8 wt %, 9 wt %, or about 10 wt %of the calcium aluminate. The amount of retarder is determined by labexperimentation by measuring the thickening times using a conventionalequipment, such as a Cement Consistomer, at temperature and pressureconditions of the subterranean formation.

In some embodiments, the foamed cementitious composition includes aviscosifier, such as a polymeric viscosifier. In some embodiments, theviscosifier can prevent settling of the calcium aluminate and/or the azoinitiator. In some embodiments, the viscosifier can improve foamstability. In some embodiments, the viscosifier is selected from amongxanthan, diutan and vinylphosphonic acid-grafted hydroxyethyl cellulose(HEC-VP). An exemplary HEC-VP includes Special Plug™, available as a 30wt % polymer slurry in a non-aqueous polyol (Special Products Divisionof Champion Chemicals, Tex.). In some embodiments, the viscosifier isxanthan. In some embodiments, the viscosifier is HEC-VP.

In some embodiments, the viscosifier is present in an amount of about0.1 wt % to about 5 wt % of the mix water used to prepare the cementcomposition. In some embodiments, the viscosifier is in an aqueoussolution. For example, the viscosifier can be about 0.1% to about 5% byweight of the mix water, such as about 0.1%, 0.5%, 0.6%, 0.7%, 0.8%,0.9%, 1%, 2%, 2.5%, 3%, 4%, or about 5% by weight of the mix water. Insome embodiments, the viscosifier is diutan and is about 0.5 wt % of themix water. In some embodiments, the viscosifier is xanthan and is about0.6 wt % of the mix water. In some embodiments, the viscosifier isHEC-VP and is about 0.8 wt % of the mix water. In some embodiments, themix water solution containing the viscosifier has a pH of 1.6. In someembodiments, the mix water solution containing the viscosifier has a pHof about 6-7.

Additional components that can be added to the cementitious compositionsdescribed herein include dispersants, set accelerators, settlingprevention additives, and the like, cement extender/filler materialssuch as flyashes, slag, silica and sand, mechanical property modifierssuch as fibers, latex materials, and rubber particles.

Also provided in this disclosure is a foamed cementitious compositionthat includes calcium aluminate, azodicarbonamide, a hydroxysultaine,SHMP, xanthan, and an amine activator selected from among CHZ and TEPA.In some embodiments, the amine activator is CHZ. In some embodiments,the amine activator is TEPA.

Method of Treating a Subterranean Formation

Additionally, provided in this disclosure is a method of treating a losscirculation zone in a subterranean formation. The method includesforming a foamed cementitious composition described herein, andintroducing the foamed cementitious composition into the subterraneanformation. In some embodiments, the foamed cementitious composition isplaced within the loss circulation zone via a wellbore. In someembodiments, the composition includes calcium aluminate, a nitrogengas-generating compound, and a foam surfactant. In some embodiments, thecomposition includes calcium aluminate, a nitrogen gas-generatingcompound, an amine activator, and a foam surfactant.

In some embodiments, the nitrogen gas-generating compound is an azocompound. In some embodiments, the azo compound is about 1% to about 10%by weight of the calcium aluminate.

In some embodiments, the composition includes an amine activatorselected from among carbohydrazide (CHZ), tetraethylenepentamine (TEPA),and hydrazine sulfate. In some embodiments, the weight ratio of the azocompound to the amine activator is about 5:1 to about 1:5.

The cementitious compositions described herein can be prepared by mixingthe cementitious solids with mix water which can be fresh water, seawater, or brine. The mix water can be premixed with gas generatingmaterials, retarders or other additives intended for slurry or setcement property manipulation to meet the requirements. Dry cementpowders, or blends mixed with solid additives are added to mix waterwith agitation. Liquid additives are injected into the mix water or intothe slurry during or after slurry preparation or while pumping theslurry downhole. Such liquid additives may include foaming compositions,foaming surfactants, or retarders and the like. After placing the foamedcomposition in the loss circulation zone, the composition is typicallyallowed to set for at least 24 hours before conducting furtheroperations such as drilling, cementing, or wellbore cleanup.

Also provided herein is a method of servicing a loss circulation zone.In some embodiments, the loss circulation zone is fluidly connected to awellbore. The method includes providing a foamed cementitiouscomposition including calcium aluminate; a nitrogen gas-generatingcompound; an amine activator; and a foam surfactant, within a portion ofa subterranean formation containing the loss circulation zone.

In some embodiments, the composition is introduced into a subterraneanformation containing the loss circulation zone using a pump.

In some embodiments, the cement compositions used herein are notdesigned for the purpose of primary cementing operations, wherein thecement slurry is placed behind a casing and allowed to set to formannular sealant between two casing strings or a casing and formation.

EXAMPLES

A series of calcium aluminate-based cements were prepared and tested asdescribed in Examples 1 and 2. The compositions were prepared byexposing anhydrous calcium aluminate to water to form slurries ofcalcium aluminate hydrates.

Other components of the compositions included: azodicarbonamide; anamine activator/accelerator compound, including carbohydrazide,tetraethylenepentamine (TEPA), and hydrazine sulfate; a foamingsurfactant, including alky sulfate salts, in which the alkyl group has aC₁₂-C₁₄ carbon chain, a betaine, a hydroxysultaine, or a combination ofsurfactants; a set retarder, including sodium hexametaphosphate (SHMP),sodium citrate, sodium tetraborate, and pentasodium salt of aminotri(methylene phosphonic acid) (Na₅ATMP) (Dequest 2006®, a 40% solutionfrom Italmatch USA, Red Bank, N.J.); and a polymeric viscosifier,including xanthan, diutan, and vinylphosphonic acid-grafted cellulose(HEC-VP) (available as a 30 wt % polymer slurry in a non-aqueous polyolavailable from Special Products Division of Champion Chemicals, Texasunder the trade name Special Plug). The diutan and xanthan solutionswere prepared as 0.5 wt % and 0.6 wt % solutions, respectively, bydissolving the polymer is water with mild agitation to minimize shearinduced polymer chain scission. The Special Plug product solution wasprepared by stirring 12.5 mL of the polymer slurry in 400 mL water,followed by addition of 1.25 mL concentrated hydrochloric acid to obtaina 0.9% polymer solution with a pH of 1.6.

Example 1—Cement Compositions Containing a Gas Generating Compound andVarious Activators

To 66 g of a 0.8 wt % solution of xanthan, 66 g of calcium aluminatecontaining ≥68.5% alumina and ≤31% CaO (sold under the trade name SECAR71, Kerneos, Va.), 2 g sodium hexametaphosphate (SHMP), 2 gazodicarbonamide, and 2.6 mL of a cocoamidopropyl hydroxysultainesolution (48 wt % in water) were added and stirred to obtain ahomogeneous suspension. The density of the slurry was 1.47 g/cc (12.2pounds per gallon). The slurry was divided into four 26 g (18 mL)batches (each batch contained 0.37 g azodicarbonamide) and placed infour Humboldt 2″×4″ cardboard cylinder molds. Gas generation activators(carbohydrazide, tetraethylene pentaamine (TEPA), andcarbohydrazide/encapsulated potassium peroxysulfate) were added to threeof the four cylinders. Into one cylinder, 0.38 g carbohydrazide wasadded; into a second cylinder, 0.38 g TEPA was added; and into a thirdcylinder, a mixture of 0.38 g carbohydrazide and 0.38 g encapsulatedpotassium peroxysulfate (K₂S₂O₈) was added. The fourth cylinder was usedas a control sample. The cylinders were kept in a water baththermostated at 140° F. for 3 days. The volumes of the foamed solidswere measured by equivalent volumes of water to match the volumes of thesolid. The results are shown in Table 1.

TABLE 1 Activator Final Gas % gas vol. amount vol. vol. in setComposition Activator (g) (mL) (mL) cement 1a None 0   56 38 68 1bCarbohydrazide 0.38 80 62 78 (CHZ) 1c TEPA 0.38 58 40 69 1d CHZ + 0.38 +0.38 80 62 78 encapsulated (0.76) K₂S₂O₈

The results showed that amine compounds functioned as activators forazodicarbonamide and increased generation of nitrogen gas. The resultsalso showed that oxidizer (K₂S₂O₈) did not increase the gas amountscompared to the amine activator by itself.

Example 2—Cement Compositions Containing Various Viscosifiers

Three viscosified mixing fluids that contained either 0.6 wt % xanthan,0.5 wt % diutan, or 0.8 wt % HEC-VP solutions were prepared. The HEC-VPsolution had a pH of 1.6 and the other solutions had a pH between 6-7.To 13 mL of each viscosified solution, 0.43 g azodicarbonamide, 0.43 gcarbohydrazide, 0.40 mL cocoamidopropyl hydroxysultaine, and 0.15 citricacid were added with stirring to obtain a homogeneous liquid blend, andpreheated to 140° F. in thermostated oil baths connected to Brookfieldviscometers.

A solid blend (referred to as CAFA in FIG. 1) of 30 g calcium aluminate(SECAR 71) and 31 g Class F flyash and 3.0 g of sodium hexametaphosphate(SHMP) was prepared and divided into three equal batches of 21 g each.To each batch, 0.35 g of potassium persulfate was added. The solid blendwas added to each liquid mixture with stirring, then placed in threecentrifuge tubes. Heat evolution was determined by monitoring thetemperature increase measured with a Brookfield viscometer underquiescent conditions.

As shown in FIG. 1, the first exotherm, observed within 10-15 minutes ofall reactions, corresponded to gas generation confirmed by visualobservations. The second exotherm, observed in the 30-45 min range, mayreflect heat of hydration of calcium aluminate. The separation betweenthe first and second exotherm was less distinct in the HEC-VP fluidblend, possibly due to the low pH of the fluid.

While xanthan and diutan showed distinct exotherms, corresponding toexothermic gas formation within 15 minutes, followed by a secondexotherm at about 40 min., corresponding to hydration of calciumaluminate, HEC-VP showed the exotherms for both gas generation andcement hydration were not well separated. This difference may be due tothe different pH values of the mix water containing the HEC-VP solutionvs. the mix water containing xanthan or diutan. The low pH value of themix water appeared to have made SHMP less effective as a retarder.

By using suitable retarders, the foamed slurry could be maintained inthe flowable/pumpable phase over the desired placement duration bydelaying the calcium aluminate hydration.

OTHER EMBODIMENTS

It is to be understood that while the invention has been described inconjunction with the detailed description thereof, the foregoingdescription is intended to illustrate and not limit the scope of theinvention, which is defined by the scope of the appended claims. Otheraspects, advantages, and modifications are within the scope of thefollowing claims.

What is claimed is:
 1. A foamed cementitious composition, comprising:calcium aluminate; a nitrogen gas-generating compound; an amineactivator to accelerate generation of gas from the nitrogengas-generating compound, the amine activator comprising anethyleneamine; and a foam surfactant.
 2. The composition of claim 1,comprising a viscosifier comprising xanthan or diutan, or both, andwherein the calcium aluminate comprises greater than or about 68.5%alumina and less than or about 31% calcium oxide.
 3. The composition ofclaim 1, wherein the foam surfactant is selected from the groupconsisting of an alkyl sulfate salt with a C₁₂-C₁₄ carbon chain, abetaine, and combinations thereof.
 4. The composition of claim 1,wherein the foam surfactant comprises cocoamidopropyl hydroxysultaine.5. The composition of claim 1, wherein the nitrogen gas-generatingcompound is an azo compound.
 6. The composition of claim 5, wherein theazo compound is azodicarbonamide.
 7. The composition of claim 5,comprising a polymeric viscosifier, wherein the azo compound is about 1%to about 10% by weight of the calcium aluminate, and wherein the amineactivator further comprises hydrazine sulfate.
 8. The composition ofclaim 5, wherein the ethyleneamine comprises ethylenediamine (EDA),diethylenetriamine (DETA), triethylenetetramine (TETA), ortetraethylenepentamine (TEPA), or any combinations thereof.
 9. Thecomposition of claim 8, wherein the weight ratio of the azo compound tothe amine activator is about 5:1 to about 1:5.
 10. The composition ofclaim 8, wherein the ethyleneamine comprises TEPA.
 11. The compositionof claim 5, further comprising a set retarder selected from the groupconsisting of hexametaphosphate, sodium borate, sodium citrate, citricacid, and an aminophosphonate, wherein the azo compound comprises aderivative of azodicarboxylic acid.
 12. The composition of claim 11,further comprising a viscosifier, wherein the derivative comprises estercomprising at least one of diisopropyl azodicarboxylate (DIAD) ordiethyl azodicarboxylate (DEAD).
 13. The composition of claim 1, furthercomprising a filler comprising at least one of fly ash, sand, clay, orvitrified shale.
 14. The composition of claim 13, wherein thecomposition does not contain an oxidizer, wherein the filler comprisesfly ash, and wherein the foam surfactant comprises a surfactant solutionin at least one of water or alcohol.
 15. The composition of claim 1,wherein the composition does not contain calcium silicates, and whereinthe foamed cementitious composition to generate an amount of gas of 65%to 90% by volume of the foamed cementitious composition.